Airtightness is the most important property of building envelopes to understand the ventilation. Airtightness refers to the flow measurement through the building envelope as a function of pressure across the building envelope. This relationship often fits to a power law, which is the most common way of expressing data. However, pressure homogeneity during airtightness tests can crop up, especially in large buildings. Recently, as buildings have become larger and higher, air infiltration and leakage have increased, leading to a growing awareness of the energy and environmental problems caused thereby. In addition, poor airtightness might lead to large infiltration rates and corresponding energy consumption, draught problems, reduced acoustical performance and dysfunctioning HVAC (Heating Ventilation and Air Conditioning) systems.
The present work deals with a numerical study and an experimental protocol to identify parameters likely to influence the pressure distribution during an airtightness test in a large building. To prevent the test from being stated improper, the French standard (NF EN ISO 9972, 2015) and its application guide (FD P50-784, 2016) require checking the pressure distribution throughout all the building during the test. Pressure deviations inside the building during the airtightness test should not be more than 10% of the building pressure differential. To better identify these parameters, air leaks were modelled either as an equivalent air gap or by real air leaks. To achieve the aim seeked, an experimental study was conducted in a single family house. Afterwards, these parameters were tested via numerical models using the commercial code Comsol Multiphysics. Note that the wind effects and outside temperature have been neglected and all walls have been considered watertight. Besides, the flow is steady and laminar. The obtained results show that the homogeneity of the pressure is influenced when the air leakage is located in an incorrectly connected location and/or the leak is located in one place. Indeed, parts that are poorly connected to the rest of the building disturb both the pressure distribution and uniformity. In such cases, additional fans must be installed in these parts to properly ensure the ventilation connection.